This week we’re back to estimating fabric yardage again, but now we’re looking at on-point quilts. If you have not read my two April blogs dealing with estimating yardage for a horizontally set quilt, it would be a good idea to go back into the archives and read those first. I’m glossing over some of the details of the process in this blog because I spent so much time on them in the two previous blogs. In general, on-point quilts take a bit more material than horizontally set quilts, due to setting blocks, side triangles, and corner triangles. If sashing and additional borders are included, the yardage increases again. Personally, I love an on-point setting. There’s just so much to work with. And while estimating the fabric yardage goes through much of the same steps as a horizontal row quilt, there are two additional steps we have to deal with – the side triangles (also called the setting triangles), and the corner triangles. Not only are both types of triangles different sizes, they are also cut differently. I’ll show you how to work with these later on in the blog.
Step One: Analyze the Main Block
We need to determine what kind of block this is. Is it a four-patch? A nine-patch?
By looking at the block’s graph on EQ8, we know it’s four block units across and four block units down, so it’s a sixteen-patch (4 x 4= 16). The block is also 10-inches finished. We have to know how large to make each block unit, so let’s divide 10-inches by 4 units per side. This give us 2 ½-inches. Each block unit in our 10-inch block will need to finish at 2 ½-inches square. We also can see that each block unit is a half-square triangle. This is good, because despite how much more complicated this block appears when compared to the Birds in the Air Block we used in the other blog, it’s actually really easy to estimate the yardage. Let’s get to it!
Step Two: Make a list of all the different types of HSTs in the block
Four HSTs in blue and white
Four HSTs in purple and white
Four HSTs in yellow and white
Four HSTs in blue and purple
There are twelve 10-inch squares in the quilt, so we know that the amounts we figure for each HST will be multiplied by 12 to give us the total.
In order to preserve the bias, we will also use the Sew and Slice method to make the HST units. This means we can get two HSTs per block unit cut from our strips.
- For the blue and white HSTs, we know they need to finish to 2 ½ inches. In order to use the Sew and Slice method, we need to add 7/8-inch to 2 ½-inches. This gives us 3.375 or 3 3/8-inches. Couple of personal issues I deal with at this point. First, I hate dealing in eighth-inch increments on a cutting mat. The lines are small and at my age and eyesight, it’s super-easy to end up with a bunch of inaccurate cuts. Second, I like to make my HSTs larger and cut them down. So, I am rounding that 3 3/8 up to 3 ½-inches. This will allow me to trim for accuracy and make the math much easier. Since there are four blue and white HSTs per block and there are 12 of these blocks in the quilt, that means I have to make 48 blue and white HSTs for this quilt. Working with 40-inches of usable fabric and cutting 3 ½-inch blocks, we divide 40 by 3 ½ and know we can get 11.42857 squares per 3 ½-inch strip. Round that down to 11. We also know we can get two HSTs per 3 ½-inch square, so we can divide the 48 needed by 2. We need to determine how much blue fabric we need for twenty-four 3 ½-inch squares. To find this out, divide the 24 squares needed by the 11 squares we can get per strip. This gives us 2.181818 – or three 3 ½-inch strips. Multiply 3 ½ by 3 and then divide by 36 inches per yard to get the amount of blue fabric required – 3 ½ x 3 = 10 1/2
10.5/36 = .291667
or 1/3 yard of blue fabric. Put that amount on your fabric chart. I will also add 1/3 yard to the white fabric on my chart, since the other half of this HST is white.
- There are also four purple and white HSTs in a block, so the math is just a repeat of what we did for the four blue and white HSTs (I told you this block was super-easy).
4 purple and white HSTs x 12 blocks in the quilt = 48 purple/white HSTs
40 inches usable fabric/3 ½-inch blocks – 11 (rounded down)
2 HSTs per 3 ½-inch block cuts the 48 needed in half to 24
24 squares/11 squares per 3 ½-inch strip = three 3 ½-inch strips
3 ½ x 3 strips needed = 10.5
10.5/36 = .291667 or 1/3 yard
We need 1/3 yard of purple fabric and another 1/3 yard of white fabric, since the other half of the purple HST is white. Taking what we know and moving it forward to the yellow and white HST, since all of the numbers are the same, we know we need 1/3 yard of yellow material and another 1/3 yard of the white. Be sure to add all of this to your fabric chart.
- The purple and blue HSTS that form the pinwheel in the middle of the block are estimated the exact same way, but remember to add an additional 1/3-yard to the blue and an additional 1/3-yard to the purple.
- Make the HSTs and trim them down to the needed 2 ½-inches.
Step Three – Design your setting blocks
At this point, we need to return to our design concept. Do we want sashing between the on-point blocks? Do we want our setting blocks to be plain or do we want to use some connector blocks? Do we want sashing and pieced blocks? This is a personal decision, but I want to work with sashing and pieced blocks. I will use the traditional snowball block and will use non-pieced sashing, just to keep things easy right now. If I decided to piece my sashing, I would simply treat the sashing like a quilt block and estimate the fabric amounts in that same way. So right now, let’s take a look at the snowball block and work with the design of it to figure out how much yardage we need.
With this block, we’re looking at a lot of open space in the middle and blue triangles in the corners. However, when we try to “grid” this block out to find out if it’s a sixteen patch (like our primary design block), we get this:
Not a whole of help, is it? Let’s look at what we know. Since the primary design block finishes at 10-inches, we know that the snowball blocks will need to finish at 10-inches, too. That’s the easy part. But we want the triangles in the corners to match the triangles in the HSTS. We don’t want them too small or too large. What we must do at this point, is divide 10 by the number of grids on the side of the primary design block, which in this case is four – 10 divided by 4 = 2 ½. The triangles will need to fall into that 2 ½-inch grid allotment.
I’m using the Flip and Sew method to make the triangles, which is the easiest way to do corner triangles on a snowball block or flying geese. Instead of cutting triangles out, we’re cutting out squares, sewing on the diagonal, and then trimming the extra away. This method doesn’t expose the bias, so it keeps everything from stretching out of shape. To do this, we need to take the 2 ½-grid allotment and add 7/8 to it. This gives us 3 3/8. And as much as I hate working with eighths, I’m going to have to do it at this juncture because I can’t make these larger and trim them down like I did in the HSTs in the primary design block.
There are six snowball blocks, with four blue triangles in each corner. The math for this estimate will work like this:
6 snowball blocks x 4 block units for each corner = 24. We need to cut twenty-four 3 3/8-inch blocks.
Working with 40-inches of usable WOF, divide 40 by 3 3/8 and that equals 11.85185. Round that down to 11 – we can get eleven 3 3/8 blocks per strip of fabric.
Divide the number of blocks needed – 24 – by the number of blocks we can get per strip – 11—and that comes to 2.181818. Round that up to three.
To get the blue yardage needed, multiply the 3 strips by 3 3/8. This equals 10.125. Divide 10.125 by 36-inches in a yard and we get .18125 or ¼-yard. Add an additional 1/4-yard to the blue fabric on your chart.
The white fabric is a bit easier to math out. We need six 10 ½ inch squares, which will finish to 10-inches. Divide 40-inches of usable WOF by 10 ½ and we get 3.809524. We can get three 10 ½-inch squares per strip of fabric. We need six blocks, so we know we need to cut 2 strips. Multiply 10 ½-inches by 2 to get 21. Divide 21 by 36 and that comes to .583333 or 5/8-yard. Add an additional 5/8-yard to the white fabric on your chart.
Step Four – Sashing and Cornerstones
I think I want to make my sashing 3-inches, finished. The first question I must ask before I estimate yardage for this, is does 3-inches conform to the Golden Ratio? I’ll have to math it out to be certain. We multiply the size of the finished block – 10-inches – by the GR – 1.618. This gives us 16.18, which we divide by 4 (since the block has four sides). Now we have 4.045 or 4-inches. That would be the widest we could make it. When figuring the smallest sashing we could make, we come up with (10 x .618)/4 = 1.545 or 1 ½-inches. Since 3-inches falls between those extremes, I’m good to go.
We will need to cut 48 pieces of 10 ½ x 3 ½ strips of blue fabric. To determine this yardage, we need to:
Divide 40-inches of usable WOF fabric by 10 ½ (the length of the sashing strip) = 3.809524. We can get three 10 ½ sashing pieces per cut.
Divide 48 by 3 to see how many strips to cut = 16 strips
Multiply 16 by 3 ½ (the width of the unfinished sashing strip) = 56.
Divide 56 by 36 (the number of inches in a yard) = 1.555556 or 1 ½-yards. Add 1 ½ yards to the blue fabric category on your chart.
Since the sashing is 3 ½-inches wide, the cornerstones will need to be that width, too. If we look at our design, we can see we need 31, which we need to break down into 17 squares and 14 triangles. Let’s see how to cut the triangles first, because we already know how to do the squares.
I will be introducing a new number here — 1.414. What is this number? Consider it kind of the Golden Ratio for triangles. Technically it’s called the Root Mean Square (RMS) and it’s used to determine 45-degree angles. It’s also used when determining voltage, but that’s another blog for another day. Simply think of it as kind of the Golden Ratio for triangles. I’ve also heard it called “Quilter’s Cake.” To use this, we take the finished size of the block needed and multiply it by 1.414 and add 1 ¼ -inches for seam allowances. So, let’s use this to determine the triangles needed in the cornerstone setting.
We know the finished size of the cornerstone square is 3-inches. Multiply 3 by 1.414 and we get 4.23725 or 4 ¼ -inches. Now add 1 ¼-inch to 4 ¼-inch and we get 5 ½-inches. We need to cut 5 ½ -inch squares and then sub cut these twice on the diagonal for our triangles. I’m going to park this little fact right here: There will come a time in this quilt design when we divide by 1.414 to get our corner triangles for the quilt center. The reason we multiply by 1.414 and get a larger number this time is that we need to cut these triangles with their long side on the straight of grain to avoid as much stretching as possible. With an on-point quilt, any side triangles – whether they be in cornerstones or setting triangles – are multiplied by 1.414 before adding the 1 ¼-inch seam allowance.
Now for the math part. We will need to cut 5 ½-inch squares and we know we need 14 triangles. Since we get four triangles per 5 ½-inch square, divide 14 by 4.
14/4= 3 ½ — Let’s round that up to four 5 ½-inch squares. Then we divide 40 WOF by 5 ½-inches to see how many squares we can get from a strip of fabric:
40/5.5 = 7.272727. We know we need one 5 ½-inch strip of fabric. When we divide that out for yardage (5.5/36) we get .152778 or 1/8 yard. I’m making my cornerstones out of yellow fabric, so I add that to the yellow yardage.
That takes care of the triangles, now we have to work with the squares, and this should be pretty straight forward by now:
We need seventeen 3 ½-inch squares.
40 WOF / 3.5 = 11.42857
We can get eleven 3 ½-inch squares per strip, so we need two strips of yellow I order to get our 17 squares.
2 strips x 3 ½-inches = 7 inches
7-inches/36-inches in a yard = .194444 or ¼ yard. Add ¼ yard to the yellow fabric.
Step Five – Setting Triangles and Corner Triangles
If you look at this diagram of the quilt at this point, you can see we have to add some triangles along the sides and corners for our top to have even edges, so we can add borders. By looking carefully at the diagram, we can see that the triangles along the sides are larger than the triangles at the top and bottom corners. And since we’ve cut our triangle cornerstones, we are already acquainted with the math formula we need to get the side triangles right (these are also called setting triangles and often the two terms are used interchangeably).
The finished block size of our primary design block as well as our snowball blocks is 10-inches.
10 x 1.414 = 14.14 or 14 1/8-inches.
14 1/8 + 1 ¼ seam allowance = 15 5/8. We will need to cut the square to make the setting (side) triangles 15 5/8-inches. We need 10 setting triangles. Since we can get four triangles per 15 5/8-inch block, we divide 10 by 4 and get 2.5. We round that up to three –we need three 15 5/8-inch squares. To figure out how many squares we can per strip of 40-inch WOF, we divide 40 by 15 5/8. This gives us 2.56. Round that up to three. We will need to cut three 15 5/8-inches wide. Multiply 3 x 15 5/8 and that gives us 46.875 or 46 7/8 inches. I will round that up to 47. Divide 47 inches by 36-inches and we get 1 1/3-yard. Since I’m making my side triangles out of purple, I’ll add the 1 1/3-yard to the purple.
The left and right, top and bottom corner triangles are cut differently and estimated differently than the side triangles. Let’s work with the estimating first, and then I’ll explain how the cutting process works. These triangles are smaller than the side triangles, so instead of multiplying, we divide. Take the size of the finished blocks and divide by 1.414, and then add 7/8-inch for the seam allowances. In this case, these figures look like this:
10-inch finished block/1.414 = 7.072136 or 7 1/8-inches.
7 1/8-inches + 7/8-inch seam allowance = 8-inches. We need to cut our squares at 8-inches. However, instead of cutting this square twice on the diagonal, only cut it once. With this being the case – getting two triangles per 8-inch block, we need to cut two blocks to get the four needed triangles. So, let’s estimate the fabric needed.
40 WOF inches / 8 = 5 – so we only need one 8-inch strip of fabric.
8 / 36 = .222222 or ¼-yard. I need to add an additional ¼-yard to the purple fabric.
We cut these squares once on the diagonal so that the short sides of the triangles will be on the straight of grain and (hopefully) won’t stretch out of shape, as they are on the outside edges of the triangle.
Step Six – Borders
The first border added to this quilt is a solid border. It will be 6-inches in width and the vertical strips will measure 85 ½-inches and the horizontal strips will measure 67 1/8-inches. I think the blue fabric would look really nice in this position, so let’s estimate the material needed. Like our horizontal row quilt, we worked with a couple of blogs back, we will cut the borders WOF. Proceeding as normal….
Multiply 85 ½ x 2 (because we need a left and right vertical border) = 171-inches of fabric needed
171 divided by 40-inches of usable WOF = 4.275. We will need five strips of 6 ½-inch fabric.
5 strips x 6 ½-inches per strip = 32.5 inches of fabric
32.5 divided by 36-inches in a yard = .902778 or 7/8 yard. I would round that up to 1 yard and add that yardage to the blue fabric on your chart.
For the horizontal top and bottom border, we know at this point, the quilt measures 67 1/8-inches.
Multiply 67 1/8 x 2 = 134.25 or 134 ¼-inches of fabric is needed
134 ¼ divided by 40 WOF = 3.35625. We need four strips of 6 ½-inch fabric.
4 x 6 ½ = 26 inches of fabric
26 divided by 36 = .722222 or ¾ yard. You could leave this yardage or round it up to a yard. I’m rounding it up to one yard more of blue fabric and putting that on my chart.
This is how I plan on designing the last border:
I like this arrangement for a couple of reasons. If you can’t find the perfect focus fabric for the border, this design would still pull all the quilt’s colors together, and t uses up scraps. In addition, if you are making a quilt from solid colors, this is just a perfect finish. You could piece this border in color blocks just about any way you want to – it depends on how you want the quilt to look. And by now, you should certainly have the math skills to do it. At this point, the left and right side of the quilt measures 85 ½-inches. I want this last border to measure 8-inches wide, which will go nicely against the 6-inch solid blue border. I really wish I could throw in some magical math formula that could show how I came up with the proportions I designed, but in all honesty, I just played with sizes until I came up with something I liked. The purple part of the border is actually two pieces of fabric, each 29-inches long (unfinished). The yellow blocks are 15-inches long (unfinished). I did not want any of these blocks pieced, as I feared it would affect the quilt’s appearance too much. Therefore, the math works a little differently with this part.
Each of the purple strips is 29-inches x 8 ½-inches unfinished. I need four of these.
8 ½ x 4 = 34-inches
34-inches divided by 36-inches = .944444 or 1 yard. Add that to the purple material.
The yellow blocks are 15-inches long and I can get two per 40 WOF strip. So, I need two 8 ½ -inch strips of yellow.
2 x 8 ½ = 17-inches
17-inches divided by 36 inches = .472222 or ½ yard. Add that to the yellow fabric.
Now for the top and bottom borders. These are 83 3/8-inches. Since these aren’t the same size as the left and right borders, we can’t use the same size blocks as we did on the vertical borders. The first step I took with the top and bottom borders was to go ahead and figure in the blue cornerstones. Those are square, so each of those finish at 8-inches x 8-inches. Let’s estimate that yardage.
There are four cornerstones, so:
4 x 8 ½ = 34-inches
This means I can cut all four cornerstones from one 8 ½-inch strip.
8.5 divided by 36 = .236111 or ¼-yard. Add that to the blue fabric.
The purple blocks are 22 3/8-inches, finished. When we add the ½-inch seam allowance, this measurement comes to 22 7/8-inches. Once again, we will have to cut four 8 ½-inch strips for these blocks.
4 x 8 ½ = 34-inches
34-inches divided by 36-inches = .944444 or 1 yard. Add one more yard to the purple fabric.
The yellow blocks are 11 ¼-inches finished. Add ½-inch seam allowances to that and it comes to 11 2/3-inches. We can cut two of these per 8 ½-inch strip, so all we need is two additional 8 ½ strips of yellow.
2 x 8 ½-inches = 17-inches
17-inches divided by 36 = .472222 or ½-yard. Add this to the yellow fabric.
Now it’s time to add up all the fabric requirements to get the yardage.
I won’t go back over backing or binding, because those two items are estimated the same way for either on-point quilts or horizontally-set quilts. If you have questions, read back over Mathing the Yardage I and II that I posted in April.
It’s my hope that even though these blogs have been math-heavy, you realize the math isn’t hard. What I really, truly want is this to set you free as a quilter – to know that you have the skills and the ability to look at a quilt, take a quilt pattern and alter it, or design your own quilt – and estimate the yardage. Now go! Be fearless with your quilting and don’t fear the math!
Until next week, Level Up That Quilting!
Love and Stitches,
Sherri and Sam